1. Field of the Invention
A major contributor to air pollution are the combustion products of fossil fuels. Included among the combustion products is nitric oxide, which is involved in the formation of photochemical smog. The nitric oxide is oxidized in the atmosphere to nitrogen dioxide, which subsequently reacts with hydrocarbons in the presence of sunlight to form photochemical smog.
Combustion products from automotive internal combustion engines, fossil fuel power plants, process furnaces, incinerators, and the like all contribute to the production of nitric oxide. Control of nitric oxide production has been directed toward modifications in the combustion process or removal of the nitric oxide from the combustion products prior to discharge into the atmosphere.
There have been numerous efforts to effectively remove nitric oxide from combustion effluents. One of the major difficulties has been that many of these devices only operate well with relatively large oxygen excess. This is true of power plant boilers, process furnaces, gas turbines, diesels, stratified charge engines, and spark ignition engines with thermal reactors. These devices generally contain flue gases with oxygen concentrations from 0.1 to 10 volume percent and nitric oxide concentrations from 100 to 4000 ppm. Thus, oxygen is present in large excess with respect to nitric oxide. While it is well known how to reduce both nitric oxide and oxygen with large quantities of a reducing agent, desirably, a process should reduce nitric oxide selectively.
2. Description of the Prior Art
U.S. Pat. No. 3,900,554 discloses the use of ammonia for reducing nitric oxide.